Repulsive nature for hydrogen incorporation to Fe₃C up to 14 GPa

We have performed in situ X-ray diffraction measurements under high pressure and high temperature to study hydrogen solubility in Fe3C carbide. Hydrogen solubility can be estimated from a volume expansion associated with hydrogen incorporation into metal. The lattice volumes and phase relations of Fe₃C-H system and Fe₃C were measured up to 14 GPa and 1973 K. The lattice volumes of Fe₃C measured in this study are well fitted using the 3rd order Birch-Murnaghan equation of state with the reported elastic parameters of Fe₃C. Obtained lattice volumes of Fe₃C-H are quite consistent with those of Fe₃C. No difference between the melting temperatures of Fe₃C-H and Fe₃C was observed. These results demonstrate that hydrogen incorporation into Fe₃C does not occur and hydrogen is unlikely to coexist with carbon in iron-alloy up to 14 GPa.